MC	Chemistry	Standard: 05
Objective: 02. Recognize that certain reactions achieve a state of dynamic equilibrium.
ILO:

For any chemical reaction at Òdynamic equilibrium,Ó the rate of the forward reaction is

a. less than the rate of the reverse reaction

b. greater than the rate of the reverse reaction

c. equal to the rate of the reverse reaction

d. unrelated to the rate of the reverse reaction

Correct Answer: c

MC	Chemistry	Standard: 05
Objective: 02. Recognize that certain reactions achieve a state of dynamic equilibrium.
ILO:

Which statement correctly describes a chemical reaction at equilibrium?

a. The concentrations of the products and reactants are equal.

b. The concentrations of the products and reactants are constant.

c. The rate of the forward reaction is less than the rate of the reverse reaction.

d. The rate of the forward reaction is greater than the rate of the reverse reaction.

Correct Answer: b

MC	Chemistry	Standard: 05
Objective: 02. Recognize that certain reactions achieve a state of dynamic equilibrium.
ILO:

In a reaction that is in Òdynamic equilibrium,Ó which factors must be equal when the reaction is at equilibrium?

a. rate at which reactants are formed and rate at which products are formed

b. concentration of reactants and concentration of products

c. potential energy of reactants and potential energy of products

d. activation energy of reactants and activation energy of products

Correct Answer: a

MC	Chemistry	Standard: 05
Objective: 02. Recognize that certain reactions achieve a state of dynamic equilibrium.
ILO:

In a reversible reaction, dynamic equilibrium is attained when the

a. rate of the forward reaction is greater than the rate of the reverse reaction

b. rate of the reverse reaction is greater than the rate of the forward reaction

c. concentration of the reactants reaches zero

d. concentration of the products remains constant

Correct Answer: d

MC	Chemistry	Standard: 05
Objective: 02. Recognize that certain reactions achieve a state of dynamic equilibrium.
ILO:

Given the reaction:

N₂(g) + 3H₂(g) 2NH₃(g) + 22.0 kcal

When equilibrium is reached in this system, the rate of the forward reaction is

a. less than the rate of the reverse reaction.

b. greater than the rate of the reverse reaction.

c. equal to the rate of the reverse reaction.

d. unrelated to the rate of the reverse reaction.

Correct Answer: c

MC	Chemistry	Standard: 05
Objective: 02. Recognize that certain reactions achieve a state of dynamic equilibrium.
ILO:

Which statement best describes a chemical reaction when it reaches dynamic equilibrium?

a. The concentrations of reactants and products are the same.

b. The concentrations of the reactants decrease to zero.

c. The forward and reverse reaction rates are the same.

d. The forward reaction rate decreases to zero.

Correct Answer: c

MC	Chemistry	Standard: 05
Objective: 02. Recognize that certain reactions achieve a state of dynamic equilibrium.
ILO:

Given the equilibrium reaction at STP:

N₂O₄(g) 2NO₂(g)

Which statement correctly describes this system?

a. The forward and reverse reaction rates are equal.

b. The forward and reverse reaction rates are both increasing.

c. The concentrations of N₂O₄ and NO₂ are equal.

d. The concentrations of N₂O₄ and NO₂ are both increasing.

Correct Answer: a

MC	Chemistry	Standard: 05
Objective: 02. Recognize that certain reactions achieve a state of dynamic equilibrium.
ILO:

Use the following equilibrium reaction to answer the following question:

H₂(g) + I₂(g) --> 2HI(g) + Heat

Which of the following would happen if the concentration of the iodine (I₂) reactant were increased?

a. more HI and heat would be produced.

b. less HI and heat would be produced.

c. more H₂ would be produced.

d. the amount of heat produced would decrease.

e. the pressure of the reaction would increase.

Correct Answer: a

MC	Chemistry	Standard: 05
Objective: 02. Recognize that certain reactions achieve a state of dynamic equilibrium.
ILO:

Carbonated soft drinks contain carbon dioxide (C0₂), which combines with water (H₂0) to form carbonic acid (H₂C0₃). If the lid of an opened carbonated drink is left off for several hours, what affect would that have on the equilibrium reaction and the contents of the bottle?

HO (l) + CO₂ (g) --> HCO₃ (aq) + Heat

a. shift left and more carbon dioxide and more water

b. shift left and less carbon dioxide and more water.

c. shift left and more carbon dioxide and less water.

d. shift left and the contents would have flowed over.

e. shift right and more carbonic acid.

Correct Answer: b

MC	Chemistry	Standard: 05
Objective: 02. Recognize that certain reactions achieve a state of dynamic equilibrium.
ILO:

Given the reaction:

A₂(g) + B₂(g) 2AB (g) + heat

An increase in the concentration of A₂(g) will

a. decrease the production of AB(g)

b. decrease the frequency of collisions between A₂(g) and B₂(g)

c. increase the production of B₂(g)

d. increase the frequency of collisions between A₂(g) and B₂(g)

Correct Answer: d

MC	Chemistry	Standard: 05
Objective: 02. Recognize that certain reactions achieve a state of dynamic equilibrium.
ILO:

Given the equilibrium reaction in a closed system:

H₂(g) + I₂(g) + heat 2HI(g)

What will the result of an increase in temperature?

a. The equilibrium will shift to the left and [H₂] will increase.

b. The equilibrium will shift to the left and [H₂] will decrease.

c. The equilibrium will shift to the right and [HI] will increase.

d. The equilibrium will shift to the right and [HI] will decrease.

Correct Answer: c

I	Chemistry	Standard: 05
Objective: 02. Recognize that certain reactions achieve a state of dynamic equilibrium.
ILO:

Use the following reaction equation and graph to answer the next question.

H₂(g) + I₂(g) --> 2 HI(g)

1. According to the graph, as time passes, which of the following statements is true concerning the above reaction?

a. the rate of disappearance of the reactants is equal to the rate of the appearance of the products.

b. the rate of disappearance of the reactants is twice that of the rate of appearance of the products.

c. the rate of disappearance of the reactants is half that of the rate of appearance of the products.

d. the rate of disappearance of H₂ is equal to the rate of appearance of I₂.

e. the rate of disappearance of reactants and the rate of appearance of products cannot be measured or graphed.

2. According to the graph, as time passes, which of the following statements is true concerning the above reaction?

a. the rate of disappearance of the reactants is half that of the rate of appearance of the products.

b. the rate of disappearance of the reactants is twice that of the rate of appearance of the products.

c. the rate of disappearance of the reactants is equal to the rate of the appearance of the products.

d. the rate of disappearance of reactants and the rate of appearance of products cannot be measured or graphed.

e. the rate of disappearance of H₂ is equal to the rate of appearance of I₂.

Correct Answers:

1. a

2. c

I	Chemistry	Standard: 05
Objective: 02. Recognize that certain reactions achieve a state of dynamic equilibrium.
ILO:

Nitrogen dioxide can be made with the reaction of nitrogen monoxide and oxygen:

2NO_(g) + O_2(g) ¾¨ 2NO_2(g)

g=gas

Assuming that the reaction is at equilibrium, what effect would the following changes have on the equilibrium position?

1. Addition of O₂?

a. An increase in the amount of NO

b. An increase in the amount of NO₂

c. A decrease in the amount of NO₂

d. No change in the amount of NO₂

2. Decrease the concentration of NO₂?

a. An increase in the amount of NO

b. A decrease in the amount of NO

c. An increase in the amount of O₂

d. No change in the amount of O₂

Correct Answers:

1. b

2. b

I	Chemistry	Standard: 05
Objective: 02. Recognize that certain reactions achieve a state of dynamic equilibrium.
ILO:

The earth's atmosphere is composed of 78.1 % nitrogen gas (N₂), 20.9% oxygen gas (0₂) and less than 1 % carbon dioxide gas (C0₂). While many living organisms can readily use oxygen and carbon dioxide, the vast amounts of nitrogen gas in the atmosphere have not been useable, except to nitrogen fixing microorganisms.

In 1905, a German chemist named Fritz Haber discovered a process that would convert nitrogen gas (N₂) into ammonia (NH₃) by reacting it with hydrogen gas (H₂). Ammonia (NH₃) can be produced by combining hydrogen (H₂) with nitrogen (N₂) in the following equilibrium reaction:

N₂(g) + 3 H₂(g) -->2 NH₃(g) + Heat

The reaction is heavily influenced by the conditions under which it is run. Since ammonia is an important industrial chemical used for making fertilizers, two experiments were conducted to investigate new ways to economically increase ammonia (NH₃) production.

The first experiment investigated the effect of changing the pressure of the reaction while maintaining constant temperature. The following data was collected:

Table One

Pressure (kPa)	1	20	40	60	80	100
Kg NH3 Produced	1	20	33	43	50	58

The second experiment investigated the effect of changing the temperature of the reaction while maintaining constant pressure. The following data was collected:

Table Two

Temperature (¡C)	200	300	400	500	600
Kg NH3 Produced	94	68	47	27	14

The graph below displays all the data from the experiments. The data on the tables above were taken from this graph.

The most efficient temperatures used in industrial processes to produce ammonia range between 350¡C and 600¡C. The most common temperature used is 500¡C. The pressures range from 18,000 kPa to 38,000 kPa. Even higher reaction pressures would be needed if it were not for the use of catalysts such as Fe, K20, and A1203. The process is so efficient now that the main cost is for the hydrogen gas used.

The United States uses about 12,000 billion kilograms of nitrogen gas to produce 15 billion kilograms of ammonia each year. The earthÕs atmosphere contains nearly 467 billion billion kilograms of nitrogen gas. Natural bacterial decay processes convert much of the nitrogen from dead plants back into atmospheric nitrogen (N₂).

1. If the temperature of the reaction were increased to 700¡C and the pressure was maintained at 60 kPa, estimate the kilograms of ammonia (NH₃) that would be produced?

a. 50 kg

b. 40 kg

c. 30 kg

d. 20 kg

e. 10 kg

2. If the temperature and pressure of the reaction were maintained at 350¡C and 25 kPa, estimate the kilograms of ammonia (NH₃) that would be produced?

a. 83 kg

b. 71 kg

c. 58 kg

d. 43 kg

e. 32 kg

3. What combination of temperature and pressure would produce the greatest amount of ammonia in kilograms?

a. 200¡C and 20 kPa

b. 300¡C and 40 kPa

c. 400¡C and 60 kPa

d. 500¡C and 80 kPa

e. 600¡C and 100 kPa

4. What combination of temperature and pressure would produce the least amount of ammonia?

a. 200¡C and 5 kPa

b. 300¡C and 10 kPa

c. 400¡C and 20 kPa

d. 500¡C and 30 kPa

e. 600¡C and 100 kPa

5. What affect does increasing the temperature have on the following reaction?

N₂ + 3H₂ -->2NH₃ + Heat

a. Increasing the temperature is like adding a reactant.

b. Increasing the temperature favors the products.

c. Increasing temperature is like removing heat causing the reaction to shift to the right.

d. Increasing temperature is like adding heat, which causes the reaction to shift to the left.

e. Increasing the temperature causes an increase in pressure, thus lowering the amount of ammonia (NH₃) produced.

6. As the temperature is increased on the reaction, what happens to the amount of nitrogen (N₂) present?

N₂+3H₂-->2NH₃+Heat

a. it remains constant

b. it increases

c. it decreases

d. it first increases and then decreases

e. it first decreases and then increases

Correct Answers:

1. e

2. c

3. a

4. d

5. d

6. c

I	Chemistry	Standard: 05
Objective: 02. Recognize that certain reactions achieve a state of dynamic equilibrium.
ILO:

A group of students read in their textbook that "increasing the temperature of a reaction would increase the rate at which the reaction occurred". They wanted to verify this statement, so they ran a reaction at various temperatures and graphed their data.

1. What would a valid conclusion be based on the results obtained?

a. increasing the temperature increased the amount of product.

b. decreasing the temperature increased the amount of product.

c. increasing the time decreased the amount of product.

d. decreasing the time increased the amount of product.

e. temperature has no effect on reaction rates

2. What would a valid conclusion be based on the results obtained?

a. decreasing the temperature decreased the amount of product.

b. increasing the temperature increased the amount of product.

c. increasing the temperature decreased the amount of product.

d. decreasing the time increased the amount of product.

e. temperature has no effect on reaction rates

3. Do the results of the experiment support the statement that "reaction rates increase as the temperature increases"?

a. no, in this case the reaction rate actually decreased.

b. yes, in this case the reaction rate did increased.

c. no, the reaction rate increased at low temperatures and decreased at high temperatures.

d. yes, the reaction rate decreased at low temperatures and increased at high temperatures.

e. changing the temperature had no effect either way

Correct Answers:

1. b

2. c

3. a